1. Field of the Invention
The present invention concerns a device for assisting an aircraft crew during changes in flight altitude.
2. Description of the Related Art
Aircraft crews are regularly led to seeking changes in flight altitude in particular on long haul flights, to optimise the performance of the aircraft, to avoid heavy traffic or adverse weather conditions.
These changes require authorisation from an air traffic controller often over-burdened with requests and giving fairly low priority to these types of manoeuvres.
Additionally, such manoeuvres are very often requested in oceanic spaces in which controllers are in charge of very large areas and communicate via HF link, which entails strong latency in the processing of requests.
The crew must therefore be well aware of the tactical situation i.e. the status of surrounding traffic so that a request is emitted at the best expedient moment thereby maximising the chances of receiving clearance from the controller.
In the remainder of the description, abbreviations, acronyms and English expressions recognised as such in the aeronautics field will be used for reasons of clarity.
Therefore in the remainder of the description the following expressions in particular are used:                ADS-B (Automatic Dependent Surveillance-Broadcast) which is a system enabling direct data exchanges between aircraft on their status (identification, position, or speed, etc.). ADS-B OUT capability is used for an aircraft capable of emitting such data, and ADS-B IN capability for an aircraft able to receive and use the data emitted by other aircraft.        AFCS (Automatic Flight Control System), a system managing the aircraft's automatic flight.        ATSA-ITP (Airborne Traffic Situational Awareness-In Trail Procedure), a procedure allowing more frequent changes in flight altitude, despite relatively heavy traffic, provided a certain number of criteria are verified. This procedure is one of the first procedures to come into force drawing advantage from ADS-B capabilities.        Clearance, which is the authorisation received from air traffic control allowing the conducting of a manoeuvre as indicated above.        CPDLC (Controller-Pilot Data Link Communications), which is a system allowing communication with the air traffic controller, based on an exchange of messages of <<SMS>> type containing standardized phraseology.        Longitudinal separation distance which is the procedural distance that an aircraft must maintain with a preceding aircraft, on instruction given by the controller. These distances may vary from one air space to another.        Flight Level/FL which is the altitude followed by aircraft in cruising phase, calculated in hundreds of feet (FL340=34000 feet for example) in increments of 10 or 20 depending on the airspace concerned.        
As part of the awareness of the aforementioned tactical situation, the crew is traditionally informed of this situation, but solely in the horizontal plane via a Cockpit Display of Traffic Information—CDTI, even, to a lesser extent via a Traffic Collision Avoidance System—TCAS. The flight levels or FLs of surrounding aircraft can also be provided, but it is up to the crew to reconstruct the situation in the vertical plane, by cross-checking the different available data.
However, faced with the constant increase in air traffic, a new procedure has been developed to facilitate changes in flight level.
This procedure called ATSA-ITP for <<Airborne Traffic Situational Awareness-In Trail Procedure>> is described in ED-159 <<Safety Performance and Interoperability Requirements Document for ATSA-ITP Applications, Eurocae, July 2008>>.
This procedure is based on new capabilities brought by ADS-B technology: Automatic Dependent Surveillance-Broadcast.
While this procedure effectively allows changes in flight level which were impossible up until now with regulations in force, it nevertheless requires much more fine-tuned analysis of the tactical situation and the transmission of additional information to the controller such as the longitudinal separation minima or the identifiers of surrounding aircraft.
It will therefore be understood that the existing systems are not the most intuitive and hence are potentially sources of interpreting errors.
In addition, no assistance is given to the crew for transmitting the necessary data to the air controller, the crew either having to enter this data manually or to transmit the same to the controller via radio, which may also be an additional source of error at the time of data transmission.